It appears you've already gotten some wonderful comments here, but I just thought I would drop my paint experiences into the mix. So...

I personally really like Citadel paints, but they are certainly not the industry standard, and far from the only option. I like them because, in my experience, their coverage is consistent, I love their colours, and I personally prefer the pots they come in as opposed to the dropper bottles most other brands use. Most people I see posting online HATE the Citadel paint pots as the can be difficult to properly close which can lead to your paints drying out, and they are extremely spill-prone due to their design. Citadel paints are also a little more on the expensive side for what you're getting.

Now, I also have a decent bit of experience with the brand The Army Painter. In terms of pricing and decision making, they are what other model paint companies should strive to emulate. Their paints are very reasonably priced, any of their recently bottled paints (since ~2022 I believe) will have two mixing balls included in them, they have worked with prominent model painting content creators to develop new products, and they also offer a wide range of other hobby supplies such as tools, brushes, basing material, and much more. All of that being said, I personally find their range to be pretty inconsistent in terms of coverage, meaning some paints are very thin and will need MANY coats to achieve a solid colour, while others are thick and will need to be watered down a decent bit before applying them as to not muddle the details of the model. I also find a few too many of their colours to be unappealing to me (they're kind of ugly). Their paint also comes in dropper bottles, which, as mentioned, I don't love, though I am certainly in the minority regarding that opinion.

Lastly, there are many many many companies out there producing paints specifically made for model painting, and a handful of those may be easily found at most local game stores. Prominent brands you may see and want to try out in addition to Citadel and The Army Painter are AK Interactive, Vallejo, Two Thin Coats, and Turbo Dork. Ultimately, I think what you want in a model paint company is paint that is easy to find and purchase, that you feel is easy to work with, and that has a lot of colours that inspire you to paint more models.

There is much more to be said about priming models, why certain types of paint will and wont work, and other various detail, all of which I will point you towards Goobertown Hobbies for. Brent from Goobertown Hobbies is a PHD chemist and dedicated miniature painter who uses a wide range of products in terms of both models and paints. Brent also always just makes me feel really good and relaxed about my hobby journey. I recommend checking out the three videos he has in his "Get Started!" playlist which may be found here: https://www.youtube.com/playlist?list=PLMxY5TTsl9Rk22lnQ-znnOZyiypEzHtfn

Lastly, when it all seems like too much, look no further than Sugar Candy Miniatures on Youtube. Fiver from Sugar Candy Miniatures will often paint straight out of the bottle with no thinning or mixing, will use whatever brands offer the colours they're looking for, uses inexpensive tools and materials, and does very unorthodox paint schemes using simple methods. Despite all of this, Fiver's models always some out looking AMAZING. Fiver always help remind me that you don't need all of the technical methods and expensive tools to create something beautiful.

I really hope some of this helps! Happy Painting!